In many pyrotechnic applications, it is necessary or desirable to initiate a specified sequence of events, some of which might be simultaneous. For example, in a fireworks display it is necessary to ignite the many pyrotechnic rockets in a particular order and at a safe distance. In building demolition, a timed sequence of explosions is set off remotely in order to cause the building to collapse in a controlled manner with a minimum of damage to surrounding buildings. An emergency ejection from the cockpit of an airplane requires a first detonation of explosive bolts to separate the cockpit canopy from the plane followed milliseconds later by a second detonation of explosive devices under the pilot's seat to propel the pilot and seat out of the airplane. Once the seat is clear of the plane, a third pyrotechnic event may be required to deploy parachutes. When launching a satellite into orbit on top of a rocket, a sequence of pyrotechnic events is required to separate a rocket gantry and other linkages simultaneously from the rocket shortly after rocket ignition, to separate the various booster stages sequentially as their fuel is used up, and to deploy the satellite from the final stage.
In each instance, the pyrotechnic devices must be ignited in the correct order and with a high degree of reliability. If, for example, the explosives on one side of a building were to go off before those on the opposite side of the building, the building might fall to one side into the street or into an adjacent building, rather than collapsing into its own basement. If the pilot's seat were to be ejected from the airplane before the canopy was open, loss of life would be almost certain. It is also important that pyrotechnic events not be set off accidentally. Pyrotechnic devices are typically ignited using a large pulse of electrical energy to set off a chemical detonator It is important that small stray electrical sparks, radio frequency electrical fields or natural electrical discharges, such as lightning, do not set off the detonator.
An object of the present invention is to provide a method of initiating a sequence of pyrotechnic events in a controlled or programmed manner which is reliable and which minimizes the possibility that pyrotechnic devices would be set off accidentally or in the wrong order.